Sardine-bone construction method for large-section tunnel

ABSTRACT

This invention relates to a method for boring a large-section tunnel safely and quickly by reinforcing and improving in advance the ground over the full length of the tunnel section, which includes; boring a top drift ( 2 ) through the full length of the tunnel ( 1 ) section, drilling curved holes inclined in forward or backward directions at an angle of about 45 degrees at preset intervals from the top drift ( 2 ) along the peripheral edges of the sections of the tunnel ( 1 ) by using ordinary small bore rock drills and curved steel pipes ( 3 ), pulling off the steel pipes ( 3 ) after inserting injection pipes into the drilled holes, injecting grout into the ground surrounding the tunnel through the injection pipes to develop artificial ground arches ( 4 ), excavating the tunnel ( 1 ), advancing suspension forms ( 6 ) and placing concrete for secondary lining.

TECHNICAL FIELD

The present invention relates to a construction method for boring alarge-section tunnel safely and quickly by reinforcing and improving theground surrounding the tunnel to develop artificial ground arches.

BACKGROUND ART

A construction method for boring a tunnel through weak ground byreinforcing the ground to increase its capability of self-support andprevent the tunnel from collapsing is shown in publication of patentapplication JP-1989-137094.

In this prior art, injection holes are drilled from the face of thetunnel into the ground surrounding the tunnel toward the tunnelingdirection. Then injection pipes are inserted into the drilled holes toinject grout into the injection holes for reinforcing the groundsurrounding the tunnel. After the ground is reinforced, the reinforcedpart of the ground is excavated, and timbered and/or lined. The stepsstated above are repeated to bore the tunnel.

DISCLOSURE OF THE INVENTION

In this prior construction method, however, drilling and injecting stepsfor reinforcing the ground, and excavating and lining steps for tunnelboring have to be repeated one after another at the face, so that theconstruction works are complicated and inefficient which result in alonger construction period.

An object of the present invention is to provide a construction methodfor boring a large-section tunnel safely and quickly by reinforcing andimproving in advance the ground over the full length of the tunnelsection.

In the sardine-bone construction method for large-section tunnel (SBRConstruction Method) of the present invention, for solving the problemstated above, drifts are bored through the full length of the tunnelsection, then curved holes inclined in forward or backward directions atan angle of about 45 degrees are drilled at preset intervals from thedrifts along the peripheral edges of the sections of the tunnel by usingordinary small bore rock drills and curved steel pipes, the steel pipesare pulled off after injection pipes are inserted into the drilledholes, grout is injected into the ground surrounding the tunnel throughthe injection pipes to develop artificial ground arches, then the tunnelis excavated, suspension forms are advanced and concrete is placed forsecondary lining, whereby the tunnel is bored.

In the construction method, at first, drifts are quickly bored throughthe full length of the tunnel section. Then curved holes are drilled byusing rock drills and curved steel pipes, the steel pipes are pulled offafter injection pipes are inserted into the drilled holes, grout isinjected into the ground surrounding the tunnel through the injectionpipes. Because these steps are executed from the drifts, the works areefficiently completed. It is different from doing the works at the faceat intervals of excavating.

In addition, drilling curved holes and injecting grout can besimultaneously executed at more than one places so that the artificialground arches are quickly developed, since the steps of reinforcing andimproving ground are executed after the drift is bored through the fulllength of the tunnel.

At the face, only excavating and lining steps are continuously executed,so that the boring works are uncomplicated and efficient.

A top drift is suitable for developing artificial ground arches when thetunnel is bore d by adopting an upper half section advancing excavationmethod.

If drifts are placed in the middle of the side-walls of the tunnel,curved holes are drilled upward along the peripheral edges of thesection of the tunnel from the drifts to the top of the tunnel. This issuitably used for excavating upper half unit of the tunnel through weakground.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a drawing explaining an embodiment of a sardine-boneconstruction method for large-section tunnel according to the presentinvention, which is sectional view of a large-section tunnel having atop drift.

FIG. 2 is a drawing showing a large-section tunnel having a top drift,which is a schematic perspective view.

FIG. 3 is a drawing explaining curved-hole-drilling by using rock drillsand curved steel pipes.

FIG. 4 is a sectional view of a large-section tunnel having drifts inthe side walls of the tunnel.

BEST MODE FOR PRACTICING THE INVENTION

The present invention is to be explained for an embodiment of thepresent invention.

When a large-section tunnel 1 is bored, at first, a top drift 2 about 5m wide is bored swiftly through the full length of the tunnel 1 by usingexcavating machines such as a tunnel boring machine (TBM) or a side typeroad header (RH).

Then curved holes are drilled along the peripheral edges of the sectionof the tunnel 1 by using ordinary rock drill 20 and curved steel pipes3. In this step, curved steel pipes, 120 mm across and about 1.5-2.0 mlong, are connected in accordance with the advance of drilling.

After injection pipes such as Mannschet tube (not shown) are insertedinto the drilled holes, the curved steel pipes 3 are pulled off, andgrout is injected into the ground surrounding the tunnel through theinjection pipes to develop artificial arches 4.

In the injection step, high pressure cement grout is injected into theground using double pipes double packers to reinforce the ground to 3MPa or higher in uniaxial compression strength within the area of about2 m outside from the injection pipes.

Intervals of the injection pipes toward the tunneling direction aredetermined in the range of 1.5-2 m according to the conditions of theground. Directions of the injection pipes are inclined by drillingcurved holes forward or backward about 45 degrees in connection with thecurvature of curved holes.

The artificial ground arches 4 shaped like sardine-bones, shown in FIG.2, are developed over the arch of the tunnel 1 by execution of the stepsstated above.

After the artificial ground arches 4 are completed, the upper half unit1A of the tunnel 1 is excavated in the rate of 1.5-3 m/cycle. Usually,the ground having 150 MPa class strength are excavated mechanically byusing large type breakers (Bk) and side type road headers (RH).

Soon after the excavation, the suspension forms 6 are advanced and quicksetting concrete mixed with 40-50 kg/m³ of steel fiber is placed forcompleting secondary lining of arch unit 7.

Mechanical excavation is also preferable for excavating the lower halfunit 1B. If necessary, blasting for loosening the face can be usedtogether. Shotcrete 9 and lock bolts 10 are carried out on the side wallunit 8. Steel fiber reinforced concrete generally used for lining ofside wall unit 8 and invert unit 11. Volume of Steel fiber in theconcrete is suitably adjusted. In joint grouting between upper half andlower half, materials such as low viscosity acrylate resin are injectedafter plastic pipes are set to stop water.

As described above, at first, the top drift 2 is quickly bored throughthe full length of the tunnel section. Then curved holes are drilled byusing rock drills 20 and curved steel pipes 3, the steel pipes 3 arepulled off after injection pipes are inserted into the drilled holes,grout is injected into the ground surrounding the tunnel 1 through theinjection pipes. Because these steps are executed from the top drift 2,the works are efficiently completed. It is more efficient than doing theworks at the face at intervals of excavating.

Moreover, drilling curved holes and injecting grout can besimultaneously executed at more than one places so that the artificialground arches 4 are quickly developed, because the steps of reinforcingand improving ground are executed after the top drift 2 is bored throughthe full length of the tunnel 1.

The tunnel 1 is excavated after the artificial ground arches 4 arecompleted, so that excavating works are safely executed. The upper halfunit 1A and the lower half unit IB are advanced independently, and atthe faces, only excavating and lining steps are continuously executed,so that the boring works are uncomplicated and efficient.

According to ground conditions, drifts 2L, 2R, shown in FIG. 4, can beplaced in the middle of the side walls of the tunnel 1. In this case,drifts 2L, 2R are bored through the side walls. Then curved holes aredrilled upward along the peripheral edges of the section of the tunnel 1from the drifts 2L, 2R to the top of the tunnel 1, the steel pipes 3 arepulled off after injection pipes are inserted into the drilled holes,grout is injected into the ground surrounding the tunnel through theinjection pipes to develop artificial ground arches 4. The tops of theleft-hand steel pipes and the right-hand steel pipes are not required toreach the same position.

INDUSTRIAL APPLICABIILTY

As has been described above, according to the construction method of thepresent invention, large-section tunnel can be safely and quickly boredby reinforcing and improving in advance the ground over the full lengthof the tunnel section.

What is claimed is:
 1. Sardine-bone construction method forlarge-section tunnel, wherein the method comprising steps of: boring oneor more drifts through the full length of the tunnel section; drillingcurved holes inclined in forward or backward directions at an angle ofabout 45 degrees, at preset intervals from the drifts along theperipheral edges of the sections of the tunnel by using ordinary smallbore rock drills and curved steel pipes; pulling off the steel pipesafter inserting injection pipes into the drilled holes; injecting groutinto the ground surrounding the tunnel through the injection pipes todevelop artificial ground arches; excavating the tunnel; advancingsuspension forms; and placing concrete for secondary lining. 2.Sardine-bone construction method for large-section tunnel as defined inclaim 1, wherein a drift is a top drift.
 3. Sardine-bone constructionmethod for large-section tunnel as defined in claim 1, which includesthe drifts placed in the middle of the side walls of the tunnel.